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Re: Have I found a bug?

• To: mathgroup at smc.vnet.net
• Subject: [mg84223] Re: Have I found a bug?
• From: dh <dh at metrohm.ch>
• Date: Fri, 14 Dec 2007 07:02:35 -0500 (EST)
• References: <fjtgdu$7hm$1@smc.vnet.net>

Hi Louise,

both are correct.

To check, one must get the original function by taking the derivative of 

  Log[- answer]

answer2= answer1 Sqrt[-1] = I answer1.

Log[-answer2] = Log[- I answer1]= Log[I]+ Log[-answer1]

The additional summand Log[I] is eliminated by the derivative.

hope this helps, Daniel



Louise Hoffman wrote:

> Dear readers,

> 

> When I calc. this in Mathematica 5.2

> 

> g[x_] := 1 - x^2

> h[x_] := -x

> Exp[-Integrate[ (D[g[x], x] - h[x])/g[x], x ] ]

> 

> it returns

> 1/Sqrt[-1+x^2]

> 

> where I would expect

> 

> 1/Sqrt[1-x^2]

> 

> Have I found a bug, or have I made a mistake?

> 

> Lots of love,

> Louise

>